This invention relates to acquiring images from an imaging source or device, and more particularly, relates to acquiring video images from various imaging sources or devices that employ different video formats.
While broadcast video transmission has standardized around the NTSC standards, in other areas multiple video standards or formats are employed, such as computer video displays (CGA, EGA, VGA, etc.) and medical systems (CAT scanners, NMRI systems, ultrasound systems, etc.). For these other areas, each video system (or format) is characterized by a video parameter file sheet that identifies the relevant video parameters that describe the video format, such as start sync pulses, front/back porch duration, line length, vertical timing, etc.
Because these video formats are not standardized, and new formats continue to be developed, interfacing peripheral add-ons from third party vendors is a difficult problem. As an example, a Photophone freezeframe video transmission system is coupled to a medical imaging device such as a CAT scanner and the Photophone captures still-video CAT scan images for transmission to remote facilities over telephone lines. Although the Photophone can operate with an NTSC format, it requires a video interface unit to convert the CAT scan images to the Photophone's display format, which is non-standard.
The current Photophone video interface technique uses an Adaptive Video multi-rate capture unit with a patented scan rate conversion technique based on a phase locked loop. The Adaptive Video interface is a hardware unit that is configured using the video format parameters for both the input and output video devices; for the example, the CAT scanner and the Photophone are the input and output devices, respectively. That is, configuring the Adaptive Video interface requires a video parameter file sheet. This sheet may or may not be available from the medical imaging device vendor, and once compiled may change if the vendor then later changes or modifies (upgrades) the video format.
That is, the Adaptive Video device acquires an image by employing a phase locked loop that is setup (via the input parameter file sheet) to be matched to the incoming video signal's frequency and sync pulses. The device then takes this input video and resamples it to achieve the desired output video signal. This requires converting the input signal parameters to the parameters of the desired output signal (which are again known via the output parameter file sheet). However, if the parameter file sheets are unavailable, or are not correct, then the viability of this approach deteriorates.
U.S. Pat. Nos. 5,019,899and 4,743,958 relate generally to capturing video signals and using synchronizing circuitry to correctly capture a video signal. U.S. Pat. No. 4,970,581 relates to a color field sequence detector that employs a clock that is locked to the horizontal sync without using a phase locked loop means.
U.S. Pat. Nos. 4,893,319, 4,595,953and 4,847,678 generally relate to colorburst synchronization by a phase locked loop means. U.S. Pat. Nos. 4,943,857, 4,942,468, 4,887,279, 4,864,359,and 4,736,238 generally relate to synchronization analysis by means other than a phase locked loop.
Thus, there are still problems when acquiring video signals from an imaging device. That is, a large amount of complicated hardware is required to be able to acquire video signals having different formats. Accordingly, there is still a need for simple and reliable hardware to acquire video signals having different formats.
These and other limitations and disadvantages of the prior art are overcome by the present invention, however, and methods and apparatus are provided for acquiring video images from video imaging devices having different video formats.